BugTraq
Re Re: PHP 5.2.4 <= various mysql functions safemode & open_basedir bypass Sep 12 2007 09:31AM
laurent gaffie gmail com
Hi Ronald

"Two years ago, I wrote a semi similar post to this one, but, well,
I'm old and tired of seeing this now. Time for folks to upgrade.

On Sep 10, 2007, at 9:38 PM, laurent.gaffie (at) gmail (dot) com [email concealed] wrote:

> Application: PHP <=5.2.4
> Web Site: http://php.net
> Platform: unix
> Bug: safemode & open_basedir bypass
> ======
> 2) Bug
> ======
> various mysql functions safemode & open_basedir bypass
> ( LOAD_FILE , INTO DUMPFILE , INTO OUTFILE )

Not a PHP *bug*, so much as yet another reason why "safe mode" and
"open_basedir" are fundamentally wrong ideas (and are being
terminated, with prejudice, in future PHP development). Users (and
hosting companies) are unedumacated on how the whole concepts of
permissions work, turn on something they think is "safe", and are
surprised by the results."

I totally agree on this, PHP is currently very used because it's easy to use.
You know i see the safemode function in PHP AS an anti-virus on a windows box .
"you dont know what you use , where you click, you just want it working,and "safely" ?
dont worry we will protect you ."
To me,that's all the reason to be of the "safemode".
Now in a context like this .. we can call this as a PHP *bug* even if we know that no.

> <?php
> mysql_connect("localhost", "granted_user","something");
> mysql_query("select load_file(0x2F6574632F706173737764)into
> dumpfile'/test/123.txt';");
> ?>

In this case:
PHP has basedir restrictions. ==> & safemode
Apache has directory restrictions.
....But, well, mysql?

What restrictions have you placed upon it, per user, and filesystem?

==> mysql_connect => granted_user(for load_file)/or_misconfigurated_user_perms.
(as in many case[like the into outfile/dumpfile ->
select 'hello i dont like you' into dumpfile '/bla/not_my_friend/www/index.html';
-> considering too that his www or some other folder is not properly chmoded
...as also in many many case .]

PHP offers the possibility to interact with mysql/&others
i think safemode/open_basedir should totally watch what's going to mysql
( like those "into outfile/dumpfile" , for sure "load_file" it's different,
but considering the fact that they build/integrate a "safemode" into PHP
then they should watch this kind of stuff.)

but once again .. i totally agree with your point,in a shared webhosting
context, if you start to trust theses kinds of functions and then let
some holes in the wall letting in the water, your shared env will be down
very soon .
So i guess the question should be :
"shall i let a software drive my security or shall i rtfm and start to
know what i'am doing ?"//not talking only about php here.
anyways that's another subject...

regards laurent gaffié

"Apparently, it's allowed to write to /test/, *and* the user perms
used to talk to mysql seem horribly broad, since it can get user
perms. So, since any Apache/PHP/mysql user on a shared host (or
whatever) in the above scenario can write to whatever they want from
mysql to /test/, it's fair game.

You see, any PHP library used, be it mysql, odbc, *whatever*, that
can be given arguments, *and does not filter* those arguments *in the
library*, based on per-apache-instance-per-user restrictions, can be
used to cross boundaries, escalate boundaries, etc.

Since on a shared host, it's often the case that 20. or 50, or
whatever many users have permissions (though apache and mysql) to
write to any directories that apache and mysql have write permissions
to, yes, PHP can *try* to clean up the activities involves, but it's
a fools errand.

mysql_query("select load_file (foo) into dumpfile'/
massive_directory_pool/user_i_hate/index.html;");
# if the mysql user has perms, Game over. PHP/apache isn't even
relevant anymore, if *mysql*
# has perms to write to the user's directory

So, for mental exercise: A GD library creating an "image" in another
directory, because apache and PHP trust GD? How about a PDF file? A
blog backup file?

You see, the problem *isn't* PHP, it's underlying libraries
inheriting perms, and using perms, that are not appropriate for the
purpose of isolating users.

The fix?

Give each user their own apache, their own mysql, their own chroot'ed
box (or vm/xen image..).

Since that's not gonna happen anytime soon for resellers who over-
subscribed their hardware, the current solution seems to be "point
and giggle".

-Ronabop

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